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Week 8: Input Devices

This week's assignment is to make a microcontroller board with a sensor and measure something with it.

For my final project, I hope to create a posture corrector that vibrates when a magnet gets too close to a sensor. Thus, for this week, my goal is to create a Hall magnetic sensor that outputs different numbers depending on how close a magnet is to the Hall sensor. While an accelerometer (which detects angle) may also work, I’ll try using a magnetic field sensor because it is easier to understand and I can focus on the design.

First, I made the input device board according to Neil's schematic of hello.mag.45.

Then, I installed the necessary software and drivers that work on Windows 10. For this week, I used one of the Linux computers in the lab to program my board. However, to program the board from my Windows 10 laptop, I needed these drivers and need to follow these steps:

• • USBtiny installer, which enables the USBtiny board to be read. (This may show up under Device Managers as “lib…”)
• • Coolterm: to scan serial ports and test if cable is working and connected
• • FTDI driver – VCP driver. my FTDI usb still does not work though.

1. I followed the instructions here
2. Install WinAVR, Adafruit drivers, upload FabISP firmware drivers into USBtiny device (ensure it’s recognized in Device Manager).
3. Double check Tools to ensure correct attiny45, clock speed, etc.
4. Ensure FTDI cable is inserted correctly, where the black cord (representing ground) connects throughout the board (and not into a lost area).
5. Ensure the rainbow cable is oriented correctly so that green and red lights up initially.
6. Under tools, click Serial Monitor for numbers to stream down the screen.
7. Ensure the USB is connected well. Works fine plugged in directly on left of laptop.

To troubleshoot, use multimeter to test voltage from 0-5. Continuously send 0V if no signal. If magnet value exceeds 500 (and increase voltage above around 3), then send 5V.

Then, I programmed the board as follows:

The default number is 512 without magnet. If the magnet is touching or some millimeters apart, then it reads 2 (or 1007 if it’s flipped over). The range fluctuates depending on how close the magnet is to the sensor. However, the numbers are sometimes imprecise and can fluctuate a lot even at the same place (especially when close to the magnet).

As the video shows, I have changed (using a magnet) the input signal to the input device.